1. Field of the Invention
The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus equipped with cleaning means for eliminating ink, water droplets etc. deposited on the ink discharging face of the recording head.
2. Related Background Art
In a ink jet recording apparatus, there may result dewing in the vicinity of the ink discharging apertures, for example on a surface in which said apertures are provided, depending on the temperature and other conditions of the recording head and surrounding atmosphere, due to a high moisture condition generated by the evaporation of the water contained in the ink deposited on the recording medium;
Also the ink discharging surface may be wetted by the ink bouncing back from recording medium.
Such dewing or wetting phenomenon becomes more marked in case a fixing heater is employed for accelerating the fixation of the recorded image to the recording medium, or in case of a high dot duty ratio.
Such dewing or wetting causes uneven deposition of the water droplets on the ink discharging surface, thus unevenly pulling the discharged ink droplets and giving rise to fluctuations in the discharging direction, discharging speed or particle size thereof, thereby eventually deteriorating the quality of the obtained image. Also the wetting of the ink discharging surface facilitates deposition of paper powder or dust, thus deteriorating the quality of the recorded image.
As a countermeasure for such phenomenon, there has been conducted cleaning of the ink discharging surface at suitable timing, in order to remove such dewing or wetting. A wiping mechanism utilizing a blade as the cleaning means is disclosed in the U.S. Pat. No. 4,364,065.
FIGS. 1A to 1C are schematic plan views of a conventional example of wiping ,means utilizing a blade member composed of silicone rubber or butyl rubber, suitable as the cleaning means.
In these drawings there is shown a recording head 20 positioned opposite to the recording surface of a recording medium 33, such as paper sheet or plastic sheet, and provided with nozzles for ink discharge. A carriage 16 supporting said recording head 20 is connected to a part of a driving belt 18 and is slidably supported by mutually parallel guide shafts 19A and 19B so that the recording head 20 can reciprocate over the entire width of the recording medium 33.
A discharge recovery device 26 for the recording head is provided at a position opposite to an end of the moving path of the recording head 20, for example the home position thereof. The discharge recovery device 26 is activated by an unrepresented motor and a transmission mechanism, thereby capping the recording head 20. In combination with the capping of the recording head 20 with a cap member 26A of said discharge recovery device 26, there is conducted ink suction by suitable suction means provided in the discharge recovery device 26, or ink pressurizing by suitable pressurizing means provided in the ink supply path to the recording head 20, thereby forcedly eliminating viscous ink from the discharge apertures, thus achieving discharge recovery. Also the capping protects the discharge apertures of the recording head, for example after a recording operation is terminated.
A blade 31, constituting a cleaning (wiping) member and composed for example of silicone rubber, is positioned at a side of the discharge recovery, device 26. The blade 31 is uniformly supported on both sides, with a cantilever mechanism, by a blade support member 31A, and is moved by a unrepresented motor and a transmission mechanism as in the discharge recovery device 26, thereby being capable of engaging with the ink discharging surface of the recording head 20. The blade 31 is made to protrude into the moving path of the recording head 20 at a suitable timing during the recording operation of the recording head 20 or after the discharge recovery operation by the recovery device 26, thereby wiping off the ink droplets, water droplets or other foreign matters on the ink discharge surface of the head 20 in the reciprocating motion thereof.
In the following there will be explained the wiping operation based on the above-explained structure.
FIG. 1A shows a case in which the recording head 20 moves in a direction A towards the home position after the recording operation, and the discharge recovery device 26 and the blade 31 are in a state retracted from the moving path of the recording head 20.
FIG. 1B shows a state in which the recording head 20 is stopped at the home position, and the capping member 26A of the discharge recovery device 26 engages with the ink discharging surface of the head 20, achieved by movement of said capping member 26A in direction B. The blade 31 moves with the head recovery device 26, but does not move with respect to the device 26.
FIG. 1C shows a case in which the recording head 20 moves in a direction D, from the home position to the recording start position, and the capping member 26A of the head recovery device 26 is retracted from the moving path of the recording head 20. On the other hand, the blade 31 moves in a direction C, with respect to the recovery device 26, thus protruding into the moving path of the recording head 20. Therefore, the ink discharging surface of the recording head 20 contacts the blade member 31 and is thus cleaned.
The wiping operation by the blade member 31 removes the dewing on the ink discharging surface or the wetting thereof generated by the ink bounced from the recording medium.
However, in such conventional structure, there are required complicated operations of causing the blade member to protrude in the moving path of the recording head and thereafter retracting said blade member, and complex mechanisms therefor.
Thus the German Laid-open Patent DE No. 3611666A1 proposes a method of fixing the blade in a protruding state in the moving path of the recording head at a predetermined position, for example in the vicinity of the home position, and achieving the cleaning operation by the movement of the recording head.
After having repeated the experiments with the ink jet recording employing the above-explained method, it was found that the recorded image was disturbed after prolonged use.
Further experiments revealed that this phenomenon was principally due to a change in the state of the ink discharging surface caused by the contact between said surface and the blade.
More specifically, the ink discharging surface of the recording head is usually subjected to a surface treatment for achieving uniform wettability for ink, namely water-repellent surface treatment for aqueous ink, or oil-repellent surface treatment for oily ink, thereby minimizing ink deposition on the ink discharging surface.
When this treated surface layer (ink-repellent treated) is deteriorated in function by the contact with the blade, there will result defective ink discharge, leading to disturbance in the image.